1. Field
This invention relates to energy radiation devices for medical hyperthermic purposes, and more particularly to a combined catheter, and energy applicator for treating prostatomegaly such as benign prostatic hypertrophy, prostatitis, and prostate malignancy by urethral insertion.
2. State of the Art
Hyperthermia or induced high body temperature has been considered beneficial in treating various human diseases including many types of cancer. More specifically, various types of malignant growths are considered by many researchers to have a relatively narrow hyperthermia treatment temperature range. Below a threshold temperature of about 41.5 degrees Celsius, thermal destruction of these malignancies is not possible, and in fact their growth may be stimulated. However, at temperatures above a range of about 43 to 45 degrees Celsius thermal damage to most normal body tissue cells occurs if exposure lasts for even a relatively short duration.
Many types of superficial cancers are known to respond to direct application of surface heat. Deeply located malignant growths are most difficult to heat to the desired temperature without damaging overlying healthy tissue, owing to limited penetration depth of externally applied energy, tissue blood flow, and heat transfer properties of the body. A solution to this problem has been the development of electromagnetic (EM) or ultrasound (US) radiation heating devices for inducing hyperthermia. This form of treatment is historically known as "diathermia". The EM frequency range preferred is that of the microwave range which is generally defined as that above 300 MHz, although the lower defined microwave band extends to 225 MHz.
EM or US radiation heating of subsurface growths from an exterior surface is ordinarily enabled by configuration and placement of one or more applicators and by appropriate selection of EM or US radiation frequency, phase and intensity. Nevertheless, tissue growths inside of, or in close proximity to, heat sensitive tissue or organs, are much more effectively and safely heated by EM or US radiation irradiating applicators positioned within the body as closely as possible to the growth requiring treatment.
The advantages of positioning EM or US radiation applicators relatively close to the growth to be heated by radiation include improved heating control, more localized heating, less possibility of overheating adjacent healthy tissue, and more direct treatment of the enlarged tissues causing the undesirable symptoms.
Close applicator access to certain types of diseased tissue growth is provided by surgical procedures for naturally occurring body passages such as the esophagus, larynx, prostate gland and colon. Surgical procedures enlarge the passage by cutting away the diseased tissue. Some heating methods involve placing small EM radiation applicators over the tissue or in an incision to provide direct irradiation of the growth. An illustrative type of a body passage insertable EM radiation applicator is described in U.S. Pat. No. 2,407,690 issued to Southworth. The Southworth type body passage EM applicators have been configured to cause a heating pattern that tends to be concentrated at the radiating tip of the applicator and which decreases at a usually exponential rate from the radiating or distal tip towards the proximal end of the applicator toward the power supply.
Special and difficult problems often attend growths found along natural body passages. For example, diseased tissue tends to spread around and along the passage, often in a relatively thin layer. Typically, the patient problems are confined to originate from a tissue layer which is less than one centimeter thick, and may extend as far as 6-10 centimeters along the passage. The use of Southworth type applicators result in nonuniform irradiation heating of the elongated growth. Thus, the temperature at the distal tip of a Southworth type applicator may have to be so hot that it kills surrounding healthy tissue in order to make the proximal end hot enough to kill the unwanted tissues in that zone.
Rectally inserted rigid and non-flexible antenna devices have been designed for heating of the prostate. Examples of such devices are disclosed in U.S. Pat. No. 4,601,296 issued to Yerushalmi, and a 1980 article titled "Microwave Applicators for Localized Hyperthermia Treatment of Cancer of the Prostate," by Mendecki et al., Int. J. Radiation Oncology, Biol. Phys., Vol. 6, pp. 1583 and 1588.
Yerushalmi, et al., published an article entitled "Localized Deep Microwave Hyperthermia in the Treatment of Poor Operative Risk Patients with Benign Prostatic Hyperplasia". This article described initial efforts to heat prostate cancer which involved a substantial amount of the prostate gland. The objective of the treatment described led them to utilize a rectal approach. They used cooling within the rectum to moderate the localized heating of the rectal mucosa, since the EM energy specific absorption rate (SAR) was much higher in this area near the applicator than within the central prostate area.
It should be pointed out that the urethra is usually about 2 cm from the rectal wall. In Benign Prostatic Hypertrophy (BPH) the urethral obstruction is the primary problem for the patient. It would appear unnecessary to treat only the posterior portion of the prostate with heat to relieve a problem primarily confined to the urethral area in the prostate. The concern by Yerushalmi about possible rectal mucosa damage was valid because he was introducing the heating through the rectum. With the urethral approach, rectal heating is not expected to be high because of the 2 cm distance between the urethra and the rectum. Thus, Yerushalmi's use of cooling was to protect the rectal wall from excessive heat damage from the rectal applicator.
Yerushalmi, et al. described their treatments as causing temperatures of 42 to 43 degrees C. in the prostate mass. These temperatures were measured by monitoring the urethral temperature. This temperature range was obtained after 10 to 15 minutes of heating. Each treatment session lasted for 1 hour and treatments were separated by 72 hours delivered twice per week. The patient's condition improved after 6 to 8 treatments, and they claimed the optimal total number of treatments was 12 to 15. Very low toxicity was reported in these cases. However, the article points out that "heating of normal tissue in the applicator-prostate mass path is unavoidable, since high power field energies are required in order to reach the prostatic mass."
Scheiblich and Petrowicz published an article in 1982 in the Journal of Microwave Power entitled "Radiofrequency-Induced Hyperthermia in the Prostate". The system described in the article was solely intended for treatment of cancer of the prostate and not BPH. Cancerous tumors of the prostate are usually quite large and involve a substantial portion of the prostate when they are detected. It is well know that treatment of only a portion of the tumor would not be considered sufficient therapy since the tumor would continue to grow from the untreated portions. This would lead to the same undesirable clinical outcome of uncontrolled tumor growth. Thus, it is important that a cancerous tissue treatment be of the whole volume involved in the malignant growth.
The Scheiblich et al. system described used a rectal approach which included rectal cooling with 2.5 degrees C. cooling water contacting the rectal wall to reduce the local rectal heating. They claimed that they first experimented with a small antenna that was inserted into the urethra but not enough power could be delivered into the prostate through the antenna in the urethra. The details of this design were not described so it is not possible to completely evaluate their claims. The article teaches heating from the remote rectal opening. This allowed a larger diameter antenna and longer diameter water bolus to be used producing a larger heating zone.
Helical coil designs have been used to heat tissues placed within the cylindrical opening of the coil. Such devices are disclosed in U.S. Pat. No. 4,527,550 issued July 1985 to Ruggera. This heating device was not inserted into the body. Another known apparatus is a body passage insertable applicator apparatus for EMR systems which includes a urethral inserted probe having a monopole antenna (Microwave Surgical Treatment of Diseases of Prostate, Harada et el., Urology, December 1985, Vol. XXVI, No. 6, pp. 572-576).
Also known is a helical wound coil applicator having coaxial inner and outer conductors electrically connected at an EMR input end to a conventional coaxial transmission line for transmitting high frequency EMR from a source to the applicator. The applicator coil is attached at one end of the outer conductor segment of the coaxial cable. The inner conductor is electrically connected to the other end of the applicator coil. A dielectric media is disposed between the applicator inner and outer conductors, and the outer conductor and termination end are covered by a dielectric sheath. A uniform, external electric tissue heating field is obtained along the entire length of the applicator radiator by exponentially increasing the thickness of the dielectric sheath over the termination end equal to at least half the outer diameter of the applicator. Those persons skilled in the art, desiring further information concerning this device are referred to U.S. Pat. No. 4,658,836 issued Apr. 21, 1987 to Paul F. Turner. This patent also contains a circulating fluid filled membrane separating the microwave applicator from the tissue while inserted in a natural body orifice. When this device is used it becomes difficult to directly and accurately measure the temperature of the heated tissue using a single temperature sensor which is housed inside of the applicator body or attached to the outer applicator membrane wall. This is because the detected temperature is greatly affected by the temperature of the cooling fluid, and further modified with unknown blood flow effects. Therefore, with current technology, accurate temperature control of the heated portions of the prostate gland with an applicator containing both cooling as well as microwave heating would require measurement with a temperature probe inserted into the prostate tissue. The microwave heating transmits its energy into the tissues of the prostate. The cooling using conductive heat transfer is less capable of affecting temperatures in the deeper tissues and primarily affects the temperature along the applicator tissue interface.
The use of inflatable balloon catheters is also well known in the existing art as described by H. H. Snyder in U.S. Pat. No. 2,936,761. However, the balloon in this type of catheter, often called a Foley catheter, is generally used to hold a catheter from coming out of a body cavity, rather than to position a portion of the catheter in a body passage. Another catheter device made for insertion into body passages for the purpose of measuring the temperature along such body passages was disclosed by Bernard Horn in U.S. Pat. No. 4,046,139. This device uses an inflatable balloon to position a small temperature sensor against the tissue comprising the body passage, but not to position the sensor along the passage.
A European Patent application No. 83305653.4 filed Sep. 22, 1983 by Kureha Kagaku Kogyo described a dipole coaxial applicator embedded in an insertable tube which has a thin polymer layer surrounding the heating zone of the microwave applicator which is inflated with circulating cooling fluid. The described use of the applicator is for the heating of endotract lesions. The prefix endo refers to "inside", which implies use inside of body passages. The metal wire temperature sensor placed on the surface of the fluid circulating membrane would certainly not be able to perform a direct or reliable measurement of the surrounding heated tissue, since the sensor is attached to the coolest point adjacent the applicator, the cooling fluid membrane. It is also known that the linear dipole antenna which he describes doesn't provide uniform heating along length of the antenna, thus the heating would not be very uniform along the body passage. The metal wire sensors have also been shown to modify the heating patterns around the metal wire. This is especially true when the wire is aligned with the microwave radiated electric field as shown in the preferred embodiment of that patent application. It is quite important to assure that prostate treatments are reliable and consistent to provide both safety and effective treatments. To achieve this therapeutic goal, it is important to avoid excessive heating of tissues which might result in patient pain and complications, but, at the same time, adequate temperatures must be obtained for a significant time in the targeted treatment tissues on the prostate gland. A lack of a reliable method to measure the heated prostate tissue temperature surrounding the urethra will result in inconsistent treatment results.
The international patent by Bicher WO 81/03616 describes a microwave antenna for intracavitary insertion. This apparatus contains an inflatable jacket which is filled with air and provided with air circulation tubes to provide some cooling. The air flow would have an effect of cooling the adjacent tissues, but would also result in incorrect temperature measurements of the actual surrounding tissue temperatures from the temperature sensors which are placed along the outer wall of the applicator apparatus.
Recently Diederich and Hynynen described use of a rectally inserted ultrasound array device for the treatment of prostate cancer ("Induction of Hyperthermia Using an Intracavitary Multielement Ultrasonic Applicator", IEEE Trans. on BME, Vol. 36, No. 4, April 1989, pp. 432-438). This article describes several ultrasound cylindrical sleeves along an inserted applicator body. This array construction is relatively large in diameter, so it is suitable for insertion into the rectum, but the construction requirements and application of insertion into the urethra for more local heating of the benign prostate diseases for the purpose of urinary function improvement is not taught.
The use of microwave radiometry as a means of temperature measurement with an inserted heating applicator has been described by Convert. Convert in U.S. Pat. No. 4,312,364 has described the use of an invasive microwave or electromagnetic wave heating probe which is also used to receive with a radiometric receiver, a measure of the thermal noise of the surrounding tissue and deduce therefrom the temperature of these tissues. Convert further suggests using the deduced temperature measurement to control the power emitted through a servocontrol system. The microwave antenna is represented by Convert as being inserted into the tissues of the body using a sharpened tip, hollow slotted needle. This is used to pierce the skin and penetrate into the body tissues by cutting into these tissues. After the antenna is inserted, the insertion needle can then be removed. This is called interstitial therapy where the devices are inserted by cutting into the body. This type of antenna is usually quite small in diameter to avoid the requirement of cutting a large insertion hole into the patient's body. Convert also suggests that a different type of probe may be designed for introduction into the human body by a natural route such as the esophagus. For this purpose, he suggests use of an ovoid dielectric sleeve around the antenna with permittivity similar to the coaxial dielectric, such as silicone. There is no tissue cooling means suggested or possible with the apparatus of Convert, and there is no positioning method provided for properly locating such a device at the correct treatment location. The configuration shown for insertion into the natural body passages has a solid dielectric sleeve, such as a silicone material, which would not cool the passage surface, and, as shown, would not be suitable for insertion or positioning within the prostatic urethra passage.
Other radiometric temperature measurement apparatus have been reported, but none are as closely related as the work reported by Convert, who uses them with an invasive heating device.